Fin attachment for tethered balloon structures

ABSTRACT

An improved empennage assembly for an inflatable, lighter-thanair aerostat structure having an elongated hull with a nose assembly and an empennage assembly at opposed ends thereof. The empennage assembly employs a plurality of stabilizing fins extending outwardly from the hull, with the fins having a plurality of generally parallelly disposed scalloped ribs, with internal stabilizing catenary lines being utilized to stabilize the fins and form the scalloped ribs therealong.

'PATENTEU HAR l 81975 SHEET 2 UF 4 WENTEUHARI 81915` FIG. 7

FIG.8

FIN ATTACHMENT FOR TETHERED BALLOON STRUCTURES BACKGROUND OF THE INVENTION The present invention relates generally to an improved inflatable, lighter-than-air aerostat structure having an inflatable elongated hull with nose and ernpennage assemblies disposed at opposed ends thereof. y

The improved aerostat structure of the present invention finds particular utility in tethered balloon applications.

The structural assembly of the aerostat structure comprises a hull fabricated from a fabric containing as a component, a durable film such as a stress-oriented polyethylene terephthalate reinforced with a scrim having a reticulate pattern for example, with line spacings of approximately one-quarter inch between adjacent lines. Stress-oriented polyethylene terepthalate film is, of course, commercially available as is such scrim. In a particular embodiment, it is generally preferred that polyester fibers be employed as the scrim reinforcing material, however, it is understood that other reinforcement fibers will be equally useful. The concept of the present invention involves means for stabilizing, reinforcing, and otherwise improving the empennage assembly of the aerostat structure in order to render the device more durable and stable, which results in minimizing structural deflections which occur when the structure in under load. Structural rigidity is particularly required in the horizontally extending fins. The loading is heaviest on these fins during flight.

The present invention renders it possible to achieve tailored configurations for the fins, particularly when a specific air foil configuration or section is required. In other words, the concept of the present invention makes it possible to form an aerodynamic configuration conforming to a shape, such as air foil section NACA-0015.

In the present concept, the term catenary is utilized, and it is understood that this term is being utilized in a comprehensive sense, and includes both catenary configurations as well as parabolic configurations. For example, the configuration of the scallops formed along the individual rib sections of the .foils are defined as being catenary in their configuration, it being understood that the configuration is essentially parabolic, which, in the present case, is defined broadly as a catenary configuration.

One advantageous feature of the arrangement of the present invention is the versatility available in controlling the configuration of the various air foils with the catenary lacing employed. In other words, the shape, configuration, and overall aerodynamics of the foil may be modified by merely changing the nature of the catenary lacing as it is employed. These features will, of course, become more apparent in the detailed discussion hereinafter.

ln addition to the structural stability, the improved air foil or empennage assembly provides ease of manufacturing with all rib attachments being completed on a single side panel and with two opposing side panels then being tied together with internal catenary lacing or catenary lines prior to final sealing ofthe edge seams and closure of the foil.

While the preferred material for the hull and empennage assembly is a three-member film consisting of a laminate of polyester fibers (Dacron), stress-oriented polyethylene terephthalate film (Mylar), and polyvinylfluoride film (Tedlar), it will be appreciated that other durable film arrangements may be utilized for the hull and empennage assemblies. This particular material is, of course, preferred for its high strength-to-weight ratio and also for its ability to function under various extremes of environmental conditions. Polyester fibers are available under the name Dacron, stress-oriented polyethylene terephthalate film is available under the name Mylan and polyvinylfluoride film is available under the name Tedlar," each from the E. l. duPont deNemours Corp. of Wilmington, Delaware. In a typical application, sufficient strength for most aerostat structures is found with 3.5 ounce polyester fibers bonded to one side of two layers of stress-oriented polyethylene terephthalate of 0.25 mil thickness which are bonded together to form a single member of the laminate sandwich, and with a film of 1.5 mil polyvinylfluoride being utilized as the other member.

Tethered balloon structures are frequently utilized for supporting payloads at high elevations on a temporary basis. One such use is for the purpose of deploying a temporary antenna for either transmission or reception of signals, particularly for line-of-sight signal transmission and reception.

SUMMARY OF THE INVENTION Briefly, the aerostat structure of the present invention includes an inflatable hull structure to provide the buoyancy required in the lighter-than-air craft. The hull is elongated and normally contains a ballonet to control the buoyancy, as is conventional in aerostat structures of this type. For control during mooring and other operations, a nose assembly is provided, the nose assembly being preferably prepared from aluminum or other light-weight rigid material. Also, conventional mooring lines are arranged on the structure so as to permit control during mooring and] launching. The empennage assembly is, of course, arranged so as to provide both durability and stability, with this durability and stability extending to the entire structure.

Specifically, the individual fin members forming the empennage assembly are provided with internal reinforcing members forming a scalloped contour along the ribs. The ribs extend generally in the elongated axis of the fin member, thus extending directly from the root to the tip. Catenary lines extend from anchor points located along the length of the structural members forming the rib, with these catenary lines extending between two opposed rib forming members alternately in a first opposed and then diagonally extending or diverging pattern. Alternate opposed rib-forming member pairs are preferably provided with catenary lines which extend in opposed diagonal relationship, thereby avoiding the introduction of a twist in the plane of the foil. Thus, the ultimate assembly provides a fin member fabricated from flexible film, and which is rendered rigid, durable and stable by means of internal catenary lacing when pressurized. This improvement in structure is obtained without adversely affecting the procedures normally required to assemble the fin, inasmuch as the opposed surfaces may be entirely secured together, one to another, with the proper air foil section being prepared prior to effecting the final edge seal around the tip segments.

Therefore, is a primary object of the present invention to provide an improved inflatable lighter-than-air aerostat structure with an inflatable elongated hull, and with a nose and empennage assemblies at opposed ends thereof, the empennage assembly being extremely stable, durable, and rigid under normal operating conditions.

It is yet a further object of the present invention to provide an improved empennage assembly consisting of a plurality of individual fin elements for an inflatable lighter-than-air aerostat structure, with the empennage assembly being fabricated from flexible films rendered rigid and stable by means of internal catenary lacing.

It is yet a further object of the present invention to provide an improved inflatable lighter-than-air aerostat structure having an empennage assembly consisting of horizontally disposed and vertically disposed fins, wherein the fins are provided with ribs which extend from the root to the tip, and wherein the ribs are given a scalloped configuration to provide uniform loading.

Other and further objects of the present invention will become apparent to those skilled in the art upon a study of the following specification, appended claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view illustrating an inflatable lighter-than-air aerostat structure fabricated in accordance with the present invention, and showing the hull and empennage assemblies together with tethering and mooring lines, and with a portion of the hull being shown broken away;

FIG. 2 is a sectional view of one of the fins forming the empennage assembly, taken along the line and in the direction of the arrows 2-2 of FIG. 1, with the view further showing, in phantom, the configuration of the assembly in the scalloped rib zone;

FIG. 3 is a sectional view ofthe fin illustrated in FIG. 2, and being taken along the line and in the direction ofthe arrows 3-3 of FIG. 2;

FIG. 4 is a detail elevational view, on a substantially enlarged scale, and illustrating the details of construction of the rib-forming assemblies, FIG. 4 being taken in the same plane as FIG. 2, but on a significantly enlarged scale;

FIG. 5 is a fragmentary perspective view on a significantly enlarged scale, and illustrating the detail of attachment of the catenary lines to the rib-forming means;

FIG. 6 is a detail elevational view, on a substantially enlarged scale, and illustrating the manner in which the fin is attached to the hull structure, and being taken along the line and in the direction of the arrows 6-6 of FIG. 3;

FIG. 7 is a vertical sectional view ofthe empennage assembly and illustrating the detail of web gusset support and internal lacing in the area of the inner section between the vertical and the horizontal fins; and

FIG. 8 is a detail partial sectional view taken generally along a fragmentary portion of the structure illustrated in FIG. 3, and illustrating the detail of the manner in which the individual lines are secured together in the catenary lacing.

DESCRIPTION OF THE PREFERRED EMBODIMENT directed to FIG. 1 of the drawings, it will be observed that the inflatable lighter-than-air aerostat structure generally designated 10 comprises an inflatable elongated hull 1l having a central axis extending therealong, and having a plurality of fins, including vertical 5 fins 12 and 14, and horizontal fins 13 and 15 forming an empennage assembly. The structure is fabricated from a film material such as shown at 16, with the same film material being employed throughout the structure. As indicated previously, this film is a laminate structure l0 of polyester fibers, stress-oriented polyethylene terephthalate film, and polyvinylfluoride film. The fibers are 3.5 ounce per square yard polyester fibers bonded tto one side of two individual members of stressoriented polyethylene terephthalate of 0.25 mil thickl5 ness each, which are bonded together to form a single member of the laminate sandwich. The polyvinylfluoride film is 1.5 mil film. These dimensions are appropriate for a tethered balloon structure having a volume of 350,000 cubic feet, and it will be appreciated that smaller structures may employ lighter films, while larger structures may employ heavier films, if desired.

At the forward end ofthe hull 11, nose assembly 18 is disposed. Nose assembly 18 is fabricated from aluminum and is utilized to aid in securing the aerostat structure in moored disposition. Also, shown in depending relationship from the base of the hull are tethering lines 19, along with the laterally disposed depending mooring lines, as are shown in FIG. l. The mooring of an aerostat device prepared in accordance with the present invention may be accomplished in any of a variety of conventional mooring arrangements.

In order to control the disposition of the gas forming the fill for the structure, ballonet 20 is arranged within the confines of the hull 11, with this ballonet structure being, of course, conventional in the art.

For added stability and rigidity of the empennage assembly, diagonally extendingguy lines 21-21 are arranged between mutually adjacent fin members, with these guy lines preferably being coupled to the fin at a point along one of the individual ribs.

Attention is now directed to FIG. 2 of the drawings wherein the fin member 1S is illustrated, fin 15 being the horizontal fin illustrated in FIG. I, and being covered with film or skin I6. The leading edge ofthe fin 15 is illustrated at 25, with the trailing edge being shown at 26. A plurality of elongated generally parallelly disposed catenary anchoring web means are secured to opposed inner surfaces of the side walls of fin 15 as illustrated at 27-27. These catenary anchoring web means extend generally from the root to the tip of the fin and have a generally T shaped configuration to provide an anchoring for the catenary lines which extend between mutually opposed anchoring webs.

With attention now being directed to FIG. 3 of the drawings, it will be observed that the individual catenary lines which extend from each anchoring point include diagonally dive'rging line segments 23-28, along with transversely extending line segments 29-29 which extend between opposed catenary anchoring web means 27--27. It is this combination of catenary lines which contributes to the stability of the structure, particularly stability and survivability under unusual or adverse weather conditions. As previously indicated, the individual catenary lines are preferably continuous, with the lines extending alternately in opposed, and then in diagonally extending relationship between opposed rib members. Also, as previously indicated, and

in order to avoid twist in the finished foil, alternate ribforming pairs are laced with the diagonally extending segments in opposed directions. In other words, in adjacent rib-forming pairs, the first diagonal will extend in a downwardly diagonal direction from root to tip, while the adjacent member will extend diagonally upwardly from root to tip. The array, therefore, will appear as illustrated in FIG. 3.

inasmuch as the stresses on the vertical fins are normally not as significant as those on the horizontal fins, the vertical fin members may, if desired, be fabricated with catenary lines extending in opposed directions only. This lacing arrangement is normally adequate for vertical fins, but has been found to be inadequate for structural strength in the horizontally extending fins.

Turning now to the details of construction of the catenary anchoring web means, the generally T-shaped web means is provided with an attaching web 3l secured to the leg thereof. This attachment may be accomplished by means of adhesive bonding, woven thread, or the like. The cross-member 32 of the element 27 has its outer surface secured to the inner surface of film or skin lo, as is apparent from FIG. 4.

Web anchor 3l is folded upon itself as at 33 so as to form an anchoring point with anchor web 34, which is also folded upon itself, as is indicated in the drawing, FIG. 4. A woven web pad 35 or line secured to web pad 35, or the like may be provided in order to provide an actual anchoring point for the individual catenary lines 28-28 and .Z9-29. Since each of these catenary anchoring means throughout the system are identical, one to another, any further description is not deemed necessary. In order to properly anchor the individual catenary lines in place, an anchoring line, as is illustrated in FIG. 8, such as at 50, with this line providing spaced anchoring loop zones 51-5i therealong.

Alternatively, the individual catenary lines 23-28 and 29-29 may be secured to pad 35 by means of stitching the individual lines through the pad, and then tying the free end of the line upon itself, in the form of an anchored loop. Other methods of anchoring may also be employed. The materials of construction for the catenary line 28-28 and 29-29 may be any convenient and conventional line having sufficient strength under the application of stresses. For certain applications, extruded monofilament nylon line may be adequate, while for larger structures which are inherently subject to greater stresses, braided, nylon may be required. As an alternative, braided polyester filaments may be desirable.

Attention is now directed to FIGS. 6 and 7 of the drawings wherein the manner of attaching the fin to the hull is disclosed. In this embodiment, the horizontal fin wall 16A is secured to the hull wall 16B by means ofa gas-tight sealing arrangement. Adhesive layer 40 couples the inner surface of fin 16A to angle web or angleskin 4l. The member 4l provides an air seal for the structure. Adhesive layers 42-42 and 43 provide a means for bonding T tape 44 into place in the overall bonding arrangement, while gas seal film 45 is arranged as a coverlay for the entire assembly, In FIG. 7, it will be observed that the horizontal fin extends continuously through the hull structure, thus providing sufficient strength for the skin inasmuch as the unit is integral in its construction. The horizontal fin is reinforced by means of the web gusset member 52, such as in the form of a woven cloth member or the like, with catenary lines also being employed in the manner illustrated in the segment shown at 53. In these zones, catenary lines extend both in opposed and diagonal relationship in order to provide the strength necessary to support the length of the vertical fin between both tips thereof. In other words, this arrangement assists in the transfer of the vload from the top to the bottom vertical fin.

By way of typical examples, in an inflatable lighterthan-air aerostat structure having a volume of approximately 350,000 cubic feet, the individual fins will have a length of 40 feet from root to tip, with approximately 20 scallops being provided for each rib along the length from root to tip. Inasmuch as the fin is feathered toward its trailing edge, that area ofthinner geometry will be provided with more closely spaced scallops in order to maintain the dverging angles between the diagonal catenary lines constant. Also, by way of typical dimensions, in a rib having a root to tip dimension of 40 feet, and having a leading edge to trailing edge dimension of 40 feet, 13 substantially equally spaced ribs will be provided per fin.

We claim:

1. An inflatable, lighter-than-air aerostat structure having an inflated elongated hull with a central axis, and with a nose assembly and an empennage assembly at opposed ends thereof, said empennage assembly comprising a plurality of stabilizing fins extending outwardly from said hull;

a. said stabilizing fins comprising a generally enclosed structure having Opposed spaced apart side walls of flexible film extending from the root to the tip thereof and defining said fin, the inner surfaces of said side walls of said stabilizing fins having catenary lines securing said walls together;

b. a plurality of elongated generally parallelly disposed catenary anchoring web means secured in generally oppositely disposed relationship to opposed inner surfaces of said stabilizing fin side walls and extending generally parallel to the longitudinal axis of the fin from the root to the tip thereof and having body means for anchoring said catenary lines thereto at spaced points along the length of said anchoring web;

c. said catenary lines being arranged in a geometrical pattern wherein said lines extend in coupling relationship to opposed anchoring webs, and wherein each anchoring web has a plurality of spaced anchoring points therealong with each anchoring point having at least one catenary line coupled thereto with a first segment of said catenary line extending from a first anchoring point on a first anchoring web along an axis extending generally normal to the axis of said fin to an opposed anchoring point on an opposed anchoring web and with the next adjacent catenary line segment extending from said opposed anchoring point along an axis extending diagonally outwardly from said first catenary line segment across said fin at substantially equal acute angles to the planar axis of said fin to outwardly spaced anchoring points on said first anchoring web disposed in spaced relationship from said first anchoring point to form a plurality of scalloped ribs along said fin surface.

2. The aerostat structure as defined in claim l being particularly characterized in that said stabilizing fins include two tins disposed generally horizontally of said hull.

3. The aerostat structure as defined in claiml being particularly characterized in that diagonally extending guy lines couple external surfaces of mutually adjacent fins together.

4. The aerostat structure as defined in claim l being particularly characterized in that a ballonet is disposed internally of said elongated hull. 

1. An inflatable, lighter-than-air aerostat structure having an inflated elongated hull with a central axis, and with a nose assembly and an empennage assembly at opposed ends thereof, said empennage assembly comprising a plurality of stabilizing fins extending outwardly from said hull; a. said stabilizing fins comprising a generally enclosed structure having opposed spaced apart side walls of flexible film extending from the root to the tip thereof and defining said fin, the inner surfaces of said side walLs of said stabilizing fins having catenary lines securing said walls together; b. a plurality of elongated generally parallelly disposed catenary anchoring web means secured in generally oppositely disposed relationship to opposed inner surfaces of said stabilizing fin side walls and extending generally parallel to the longitudinal axis of the fin from the root to the tip thereof and having body means for anchoring said catenary lines thereto at spaced points along the length of said anchoring web; c. said catenary lines being arranged in a geometrical pattern wherein said lines extend in coupling relationship to opposed anchoring webs, and wherein each anchoring web has a plurality of spaced anchoring points therealong with each anchoring point having at least one catenary line coupled thereto with a first segment of said catenary line extending from a first anchoring point on a first anchoring web along an axis extending generally normal to the axis of said fin to an opposed anchoring point on an opposed anchoring web and with the next adjacent catenary line segment extending from said opposed anchoring point along an axis extending diagonally outwardly from said first catenary line segment across said fin at substantially equal acute angles to the planar axis of said fin to outwardly spaced anchoring points on said first anchoring web disposed in spaced relationship from said first anchoring point to form a plurality of scalloped ribs along said fin surface.
 2. The aerostat structure as defined in claim 1 being particularly characterized in that said stabilizing fins include two fins disposed generally horizontally of said hull.
 3. The aerostat structure as defined in claim 1 being particularly characterized in that diagonally extending guy lines couple external surfaces of mutually adjacent fins together.
 4. The aerostat structure as defined in claim 1 being particularly characterized in that a ballonet is disposed internally of said elongated hull.
 5. The aerostat structure as defined in claim 1 being particularly characterized in that sealing means are disposed to couple said fins to said hull in gas-tight relationship, one to another, said sealing means including a generally T-shaped member with the bar portion coupling adjacent hull portions together and with the leg portion extending outwardly of the hull to join the fin side wall to the hull. 